The present invention relates to managing a serial link in a data processing input/output (I/O) system, and more particularly relates link-level facilities on each end of a serial link which manage the link for the transfer of data therebetween.
Data processing I/O systems are known in which data and commands are formatted into frames or packets and which are transmitted over links between channels and peripheral control units. U.S. Pat. No. 4,241,398 issued Dec. 23, 1980 to Carll for "Computer Network, Line Protocol System" discloses a line protocol format for the asynchronous exchange of digital signal information between processing units in a supervisory control system having a central processing unit and at least one remote processing unit.
U.S. Pat. No. 4,446,515 issued May 1, 1984 to Sauer et al. for "Passive Bus System for Decentrally Organized Multi-Computer Systems" discloses a passive bus system for a decentrally organized multi-bus computer system incorporating exclusively optical transmission means for data exchange operations wherein the data is formatted into information packets separated by pauses having adjustable lengths.
U.S. Pat. No. 4,675,864 issued Jun. 23, 1987 to Bliek et al. for "Serial Bus System" discloses a serial bus system in which frames are sent from a central system to a plurality of substations over a first conductor and information is sent from the substations to the central station over a second conductor. Each transmitted frame contains bits identifying whether the frame is for an address, data or a command.